Download Net Ionic Prep Session NMSI INSTRUCTOR

*
AP
Chemistry
Net Ionic Equations
René McCormick
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© 2008 by René McCormick. All rights reserved.
Net Ionic Equation Practice Site » http://dwb4.unl.edu/AP2/
Very Last Minute
AP® Net Ionic Equation
Attack Strategies
These probably won’t get you a 15 on Question 4, BUT they WILL HELP YOU BEAT THE
NATIONAL AVERAGE. The national average on this question is usually between 7—8. If you
can consistently score 11—12, that puts you WAY ahead of the game!
First, the minimum knowledge required to survive this question…
Solubility rules:
1. Big Mamma: All nitrates are soluble.
2. Big Daddy: All IA metals and ammonium salts are soluble.
3. Halides: All are soluble except silver, mercury or lead.
4. Strong acids: hydrochloric, hydrobromic, hydroiodic, nitric, perchloric, sulfuric—
WRITE THESE DISSOCIATED except concentrated sulfuric, it really is 97% H2SO4 and
3% water in the jug, so water is way outnumbered and the molecules don’t dissociate
completely. If carbonic acid is formed as a product Æ CO2 + H2O.
5. Strong bases: hydroxides [and oxides] of IA and IIA* metals—write these bases dissociated.
WRITE ALL WEAK ACIDS AND BASES AS MOLECULES—be on the look out for BF3 and
its cousins BCl3, etc. They are classic Lewis acids and when reacting with ammonia (a classic
weak Lewis base), the product is F3BNH3 (just smash everything together) since nitrogen
donated its unshared electron pair to boron in an act of extreme generosity and formed a
coordinate covalent bond. Lewis Acids Accept an electron pair.
* The “little guys” in the IIA’s have solubility issues, write Be and Mg UNdissociated—calcium
can go either way, the big guys are soluble. HF is not a strong acid since it’s the little guy as well
in the halogen series. The little guys make a stronger bond with OH− or H+ and do not dissociate
as much in water. Also remember that the IA metals are named the alkali metals and the IIA’s
are the alkaline earth metals. What does “alkaline” mean? BASIC, so put them in water as
metals, they dissolve and you make OH−. Put IA metals in water and KABOOM!
KABOOM = formation of explosive hydrogen gas, H2.
TURN THIS PUPPY OVER FOR
THE ATTACK STRATEGIES!
(1) Copyright © 2008 by René McCormick. All rights reserved. (2) AP® is a registered trademark of the College Entrance Examination Board and was not involved in the production of and does not
endorse this product. Permission is granted for individual classroom teachers to reproduce the activity sheets and illustrations for their own classroom use. Any other type of reproduction of these
materials is strictly prohibited.
Page 1
Attack Strategies
Before trying to figure out the “answers”, scan the words on question 4 (a) thru (c) and do the
following: [don’t write any products until you’ve done all SIX things!]
1. Cross out the word nitrate any time it appears on the page.
2. Circle any word that implies solid or gas. (powdered, turnings, chunk, vapor, etc.)
3. Cross out any IA metal that you see UNLESS it is associated with a circled solid or gas
word.
4. Underline halides then ask yourself if silver, mercury or lead is present—if not you can
cross the halide off as well such as with hydrochloric acid. The H+ is the reacting
species. (Bring the halide back as a reacting ion IF you need to oxidize something
halide-1 → halogen2.)
5. Circle “burned in air” or “combines with oxygen” or anything that implies combustion
and celebrate!
6. Circle the word concentrated. Get very excited if you see excess concentrated. It means
you have entered the land of complex coordinated ions (excess is not necessary, but often
appears). Sounds scary, but VERY easy. LOSE THE FEAR!
Now, focus on the reactions you just marked.
WRITE THE REACTANT SETS FOR
ALL THREE. Spend 3 minutes writing products using the solubility rules and strong acidbase guidelines listed on the other side of this page. To get the easy three points involved
with step SIX above do the following:
Write the reactants. On the product side, open a set of brackets [ ]. Put the metal ion in
the brackets first then open a set of parentheses [M ion( )]. Next put a subscript on the
parentheses that is twice the charge on the metal—I’m not proud of this, but it will earn
credit. For a +2 metal it becomes [M2+( )4]. Finally, plop the ligand inside the
parentheses and do the math to get the charge. If the ligand is ammonia or water, the
ligand is neutral, so our example carries a +2 overall charge, [M2+( )4]2+, if the ligand is
hydroxide or a halide, which are both negative one, then our example becomes
[M2+(OH)4]2−. Other ligands are possible, like SCN−, the thiocyanate ion and other
polyatomic ions you should recognize.
Additional knowledge that contributes to survival:
• metal oxides + water → bases (ask yourself strong or weak? Dissociate the strong)
• nonmetal oxides + water → acids (ask yourself strong or weak? Dissociate the strong)
• metal carbonate heated → CO2 + metal oxide
• Redox, “acidified”? H+ is a reactant and water is a product.
• React a metal with oxygen → metal oxide
• React a nonmetal with oxygen [combustion] → make oxides of the nonmetal(s), NOT always
CO2 & H2O!
Page 2
2007 AP® CHEMISTRY FREE-RESPONSE QUESTIONS
CHEMISTRY
Part B
Time—40 minutes
NO CALCULATORS MAY BE USED FOR PART B.
Answer Question 4 below. The Section II score weighting for this question is 10 percent.
4. For each of the following three reactions, in part (i) write a balanced equation for the reaction and in part (ii)
answer the question about the reaction. In part (i), coefficients should be in terms of lowest whole numbers.
Assume that solutions are aqueous unless otherwise indicated. Represent substances in solutions as ions if the
substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction.
You may use the empty space at the bottom of the next page for scratch work, but only equations that are written
in the answer boxes provided will be graded.
(a) A solution of sodium hydroxide is added to a solution of lead(II) nitrate.
(i) Balanced equation:
(ii) If 1.0 L volumes of 1.0 M solutions of sodium hydroxide and lead(II) nitrate are mixed together, how
many moles of product(s) will be produced? Assume the reaction goes to completion.
______________________________________________________________________________________
______________________________________________________________________________________
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-9-
Page 3
2007 AP® CHEMISTRY FREE-RESPONSE QUESTIONS
(b) Excess nitric acid is added to solid calcium carbonate.
(i) Balanced equation:
(ii) Briefly explain why statues made of marble (calcium carbonate) displayed outdoors in urban areas are
deteriorating.
______________________________________________________________________________________
______________________________________________________________________________________
(c) A solution containing silver(I) ion (an oxidizing agent) is mixed with a solution containing iron(II) ion
(a reducing agent).
(i) Balanced equation:
(ii) If the contents of the reaction mixture described above are filtered, what substance(s), if any, would
remain on the filter paper?
______________________________________________________________________________________
______________________________________________________________________________________
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Page 4
2007 AP® CHEMISTRY FREE-RESPONSE QUESTIONS (Form B)
CHEMISTRY
Part B
Time—40 minutes
NO CALCULATORS MAY BE USED FOR PART B.
Answer Question 4 below. The Section II score weighting for this question is 10 percent.
4. For each of the following three reactions, in part (i) write a balanced equation for the reaction and in part (ii)
answer the question about the reaction. In part (i), coefficients should be in terms of lowest whole numbers.
Assume that solutions are aqueous unless otherwise indicated. Represent substances in solutions as ions if the
substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction.
You may use the empty space at the bottom of the next page for scratch work, but only equations that are written
in the answer boxes provided will be graded.
(a) Solid ammonium carbonate decomposes as it is heated.
(i) Balanced equation:
(ii) Predict the algebraic sign of 'Sq for the reaction. Explain your reasoning.
______________________________________________________________________________________
______________________________________________________________________________________
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-9Page 5
2007 AP® CHEMISTRY FREE-RESPONSE QUESTIONS (Form B)
(b) Chlorine gas, an oxidizing agent, is bubbled into a solution of potassium bromide.
(i) Balanced equation:
(ii) What is the oxidation number of chlorine before the reaction occurs? What is the oxidation number of
chlorine after the reaction occurs?
______________________________________________________________________________________
______________________________________________________________________________________
(c) A small piece of sodium is placed in a beaker of distilled water.
(i) Balanced equation:
(ii) The reaction is exothermic, and sometimes small flames are observed as the sodium reacts with the
water. Identify the product of the reaction that burns to produce the flames.
______________________________________________________________________________________
______________________________________________________________________________________
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-10Page 6
2008 AP® CHEMISTRY FREE-RESPONSE QUESTIONS (Form B)
CHEMISTRY
Part B
Time— 40 minutes
NO CALCULATORS MAY BE USED FOR PART B.
Answer Question 4 below. The Section II score weighting for this question is 10 percent.
4. For each of the following three reactions, in part (i) write a balanced equation for the reaction and in part (ii)
answer the question about the reaction. In part (i), coefficients should be in terms of lowest whole numbers.
Assume that solutions are aqueous unless otherwise indicated. Represent substances in solutions as ions if the
substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction.
You may use the empty space at the bottom of the next page for scratch work, but only equations that are written
in the answer boxes provided will be graded.
(a) Chlorine gas, an oxidizing agent, is bubbled into a solution of potassium bromide at 25°C.
(i) Balanced equation:
(ii) Predict the sign of ΔS° for the reaction at 25°C. Justify your prediction.
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
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-10Page 7
2008 AP® CHEMISTRY FREE-RESPONSE QUESTIONS (Form B)
(b) Solid strontium hydroxide is added to a solution of nitric acid.
(i) Balanced equation:
(ii) How many moles of strontium hydroxide would react completely with 500. mL of 0.40 M nitric acid?
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
(c) A solution of barium chloride is added drop by drop to a solution of sodium carbonate, causing a precipitate
to form.
(i) Balanced equation:
(ii) What happens to the pH of the sodium carbonate solution as the barium chloride is added to it?
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
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-11Page 8
2009 AP® CHEMISTRY FREE-RESPONSE QUESTIONS
CHEMISTRY
Part B
Time— 40 minutes
NO CALCULATORS MAY BE USED FOR PART B.
Answer Question 4 below. The Section II score weighting for this question is 10 percent.
4. For each of the following three reactions, write a balanced equation in part (i) and answer the question in
part (ii). In part (i), coefficients should be in terms of lowest whole numbers. Assume that solutions are aqueous
unless otherwise indicated. Represent substances in solutions as ions if the substances are extensively ionized.
Omit formulas for any ions or molecules that are unchanged by the reaction. You may use the empty space at the
bottom of the next page for scratch work, but only equations that are written in the answer boxes provided will
be graded.
(a) A sample of solid iron(III) oxide is reduced completely with solid carbon.
(i) Balanced equation:
(ii) What is the oxidation number of carbon before the reaction, and what is the oxidation number of
carbon after the reaction is complete?
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
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-9Page 9
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2009 AP® CHEMISTRY FREE-RESPONSE QUESTIONS
(b) Equal volumes of equimolar solutions of ammonia and hydrochloric acid are combined.
(i) Balanced equation:
(ii) Indicate whether the resulting solution is acidic, basic, or neutral. Explain.
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
(c) Solid mercury(II) oxide decomposes as it is heated in an open test tube in a fume hood.
(i) Balanced equation:
(ii) After the reaction is complete, is the mass of the material in the test tube greater than, less than, or
equal to the mass of the original sample? Explain.
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
YOU MAY USE THE SPACE BELOW FOR SCRATCH WORK, BUT ONLY EQUATIONS
THAT ARE WRITTEN IN THE ANSWER BOXES PROVIDED WILL BE GRADED.
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2009 AP® CHEMISTRY FREE-RESPONSE QUESTIONS (Form B)
CHEMISTRY
Part B
Time— 40 minutes
NO CALCULATORS MAY BE USED FOR PART B.
Answer Question 4 below. The Section II score weighting for this question is 10 percent.
4. For each of the following three reactions, write a balanced equation in part (i) and answer the question in
part (ii). In part (i), coefficients should be in terms of lowest whole numbers. Assume that solutions are aqueous
unless otherwise indicated. Represent substances in solutions as ions if the substances are extensively ionized.
Omit formulas for any ions or molecules that are unchanged by the reaction. You may use the empty space at the
bottom of the next page for scratch work, but only equations that are written in the answer boxes provided will
be graded.
(a) A barium nitrate solution and a potassium fluoride solution are combined and a precipitate forms.
(i) Balanced equation:
(ii) If equimolar amounts of barium nitrate and potassium fluoride are combined, which reactant, if any,
is the limiting reactant? Explain.
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
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-9Page 11
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2009 AP® CHEMISTRY FREE-RESPONSE QUESTIONS (Form B)
(b) A piece of cadmium metal is oxidized by adding it to a solution of copper(II) chloride.
(i) Balanced equation:
(ii) List two visible changes that would occur in the reaction container as the reaction is proceeding.
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
(c) A hydrolysis reaction occurs when solid sodium sulfide is added to distilled water.
(i) Balanced equation:
(ii) Indicate whether the pH of the resulting solution is less than 7, equal to 7, or greater than 7. Explain.
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
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2008 AP® CHEMISTRY FREE-RESPONSE QUESTIONS (Form B)
Answer Question 5 and Question 6. The Section II score weighting for these questions is 15 percent each.
Your responses to these questions will be graded on the basis of the accuracy and relevance of the information cited.
Explanations should be clear and well organized. Examples and equations may be included in your responses where
appropriate. Specific answers are preferable to broad, diffuse responses.
5. The identity of an unknown solid is to be determined. The compound is one of the seven salts in the following
table.
Al(NO3)3. 9H2O
BaCl2. 2H2O
CaCO3
NaCl
BaSO4
Ni(NO3)2. 6H2O
CuSO4. 5H2O
Use the results of the following observations or laboratory tests to explain how each compound in the table may
be eliminated or confirmed. The tests are done in sequence from (a) through (e).
(a) The unknown compound is white. In the table below, cross out the two compounds that can be eliminated
using this observation. Be sure to cross out these same two compounds in the tables in parts (b), (c), and (d).
Al(NO3)3. 9H2O
BaCl2. 2H2O
CaCO3
NaCl
BaSO4
Ni(NO3)2. 6H2O
CuSO4. 5H2O
(b) When the unknown compound is added to water, it dissolves readily. In the table below, cross out the two
compounds that can be eliminated using this test. Be sure to cross out these same two compounds in the
tables in parts (c) and (d).
Al(NO3)3. 9H2O
BaCl2. 2H2O
CaCO3
NaCl
BaSO4
Ni(NO3)2. 6H2O
CuSO4. 5H2O
(c) When AgNO3(aq) is added to an aqueous solution of the unknown compound, a white precipitate forms. In
the table below, cross out each compound that can be eliminated using this test. Be sure to cross out the
same compound(s) in the table in part (d).
Al(NO3)3. 9H2O
BaCl2. 2H2O
CaCO3
NaCl
BaSO4
Ni(NO3)2. 6H2O
CuSO4. 5H2O
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-12Page 13
2008 AP® CHEMISTRY FREE-RESPONSE QUESTIONS (Form B)
(d) When the unknown compound is carefully heated, it loses mass. In the table below, cross out each
compound that can be eliminated using this test.
Al(NO3)3. 9H2O
BaCl2. 2H2O
CaCO3
NaCl
BaSO4
Ni(NO3)2. 6H2O
CuSO4. 5H2O
(e) Describe a test that can be used to confirm the identity of the unknown compound identified in part (d).
Limit your confirmation test to a reaction between an aqueous solution of the unknown compound and an
aqueous solution of one of the other soluble salts listed in the tables. Describe the expected results of the
test; include the formula(s) of any product(s).
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-13Page 14
Name: __________ ______________
Version A
Teacher: ________________________
AP* Chemistry: Net Ionic Reactions Prep Session Multiple Choice
NO CALCULATORS MAY BE USED
Note: For all questions, assume that the temperature is 298 K, the pressure is 1.00 atmosphere, and solutions are aqueous
unless otherwise specified.
Throughout the test the following symbols have the definitions specified unless otherwise noted.
Directions: Each set of lettered choices below refers to the numbered questions or statements immediately following it. Select the
one lettered choice that best answers each question or best fits each statement and then fill in the corresponding oval on the answer
sheet. A choice may be used once, more than once, or not at all in each set. Before turning in your answer sheet, count the number
of questions that you have skipped and place that number next to your name ON YOUR ANSWER SHEET and circle it.
Questions 11-14 refer to the reactions represented below.
(A)
H2SeO4(aq) + 2 Cl–(aq) + 2 H+(aq) → H2SeO3(aq) + Cl2(g) + H2O(l)
(B)
S8(s) + 8 O2(g) → 8 SO2(g)
(C)
3 Br2(aq) + 6 OH–(aq) → 5 Br– (aq) + BrO3– (aq) 3 H2O(l)
(D)
Ca2+(aq) + SO42–(aq) → CaSO4(s)
(E)
PtCl4(s) + 2 Cl– (aq)→ PtCl62– (aq)
1. A precipitation reaction
2. A reaction that produces a coordination complex
3. A reaction in which the same reactant undergoes both oxidation and reduction
4. A combustion reaction
(1) Test Questions are Copyright © 1984-2002 by College Entrance Examination Board, Princeton, NJ. All rights reserved. For face‐to‐face teaching purposes, classro om teachers are permitted to reproduce the questions. Web or Mass distribution prohibited. (2) AP® is a registered trademark of the College Entrance Examination Board. The College Entrance Examination Board was not involved in the production of and does not endorse this product. Permission is granted for individual classroom teachers to reproduce for their own classroom use. Any other type of re production of these materials is strictly prohibited.
1
Page 15
Version A
Directions: Each of the questions or incomplete statements below is followed by five suggested answers or completions. Select the
one that is best in each case and then fill in the corresponding oval on the answer sheet.
5. The net ionic equation for the reaction between silver carbonate and hydrochloric acid is
A) Ag2CO3(s) + 2 H+ + 2 Cl– → 2 AgCl(s) + H2O + CO2(g)
B) 2 Ag+ + CO32– + 2 H+ + 2 Cl– → 2 AgCl(s) + H2O + CO2(g)
C) CO32– + 2 H+ → H2O + CO2(g)
D) Ag+ + Cl– → AgCl(s)
E) Ag2CO3(s) + 2 H+ → 2Ag+ + H2CO3
6.
–
...CrO2 +
...OH–
→ ... CrO4 + ... H2O + ...
2–
7. The net ionic equation for the reaction that occurs
during the titration of nitrous acid with sodium
hydroxide is
e–
When the equation for the half-reaction above is
balanced, what is the ratio of the coefficients OH – :
CrO2– ?
A)
B)
C)
D)
E)
A) HNO2 + Na+ + OH– → NaNO2 + H2O
B) HNO2 + NaOH → Na+ + NO2– + H2O
C) H+ + OH– → H2O
1:1
2:1
3:1
4:1
5:1
D) HNO2 + H2O → NO2– + H3O+
E) HNO2 + OH– → NO2¯ + H2O
8. What is the net ionic equation for the reaction that occurs when aqueous copper(II) sulfate is added to excess
6-molar ammonia?
A) Cu2+ + SO42– + 2 NH4+ + 2 OH– → (NH4)2SO4 + Cu(OH)2
B) Cu2+ + 4 NH3 + 4 H2O → Cu(OH)42– + 4 NH4+
C) Cu2+ + 2 NH3 + 2 H2O → Cu(OH)2 + 2 NH4+
D) Cu2+ + 4 NH3 → Cu(NH3)42+
E) Cu2+ + 2 NH3 + H2O → CuO + 2 NH4+
2
Page 16
Version A
9.
6 I– + 2 MnO4– + 4 H2O(l) → 3 I2(s) + 2 MnO2(s) + OH–
Which of the following statements regarding the reaction represented by the equation above is correct?
A) Iodide ion is oxidized by hydroxide ion.
B) MnO4– is oxidized by iodide ion.
C) The oxidation number of manganese changes from +7 to +2.
D) The oxidation number of manganese remains the same.
E) The oxidation number of iodine changes from –1 to 0.
10.
. . . Cr2O72– + . . . e– + . . . H+ →
. . . Cr3+ + . . . H2O(l)
When the equation for the half-reaction above is balanced with the lowest whole-number coefficients, the
coefficient for H2O is
A)
2
B)
4
C)
6
D)
7
E) 14
11. The metal calcium reacts with molecular hydrogen to form a compound. All of the following statements
concerning this compound are true EXCEPT:
A) Its formula is CaH2.
B) It is ionic.
C) It is solid at room temperature.
D) When added to water, it reacts to produce H 2 gas.
E) When added to water, it forms an acidic solution.
3
Page 17
Version A
12.
2 H2O + 4 MnO4¯ + 3 ClO2¯ → 4 MnO2 + 3 ClO4¯ + 4 OH¯
Which species acts as an oxidizing agent in the reaction represented above?
A) H2O
B) ClO4¯
C) ClO2¯
D) MnO2
E) MnO4¯
14. Which of the following oxides is a gas at 25ºC and
1 atm ?
13. When an aqueous solution of NaOH is added to an
aqueous solution of potassium dichromate, K 2Cr2O7
the dichromate ion is converted to
A) CrO4
A)
B)
C)
D)
E)
2¯
B) CrO2
C) Cr3+
Rb2O
N2O
Na2O2
SiO2
La2O3
D) Cr2O3(s)
E) Cr(OH)3(s)
15.
True statements about the reaction represented above include which of the following?
I. Cu(s) acts as an oxidizing agent.
II. The oxidation state of nitrogen changes from +5 to +2.
III. Hydrogen ions are oxidized to form H 2O(l).
A)
B)
C)
D)
E)
I only
II only
III only
I and II only
II and III only
4
Page 18
Version A
16. Propane gas, C3H8, burns in excess oxygen gas. When the equation for this reaction is correctly balanced and all
coefficients are reduced to their lowest whole-number terms, the coefficient for O2 is
A) 4
B) 5
C) 7
D) 10
E) 22
17. Which of the following substances is LEAST soluble in water?
A)
B)
C)
D)
E)
(NH4)2SO4
KMnO4
BaCO3
Zn(NO3)2
Na3PO4
5
Page 19
NET IONIC PREP SESSION KEY
2007 Net Ionic Q4 KEY
Monday, October 27, 2008
2:41 PM
Net Ionics Page 1
NET IONIC PREP SESSION KEY
Net Ionics Page 2
NET IONIC PREP SESSION KEY
2007B Net Ionic Q4 KEY
Monday, October 27, 2008
2:42 PM
Net Ionics Page 3
NET IONIC PREP SESSION KEY
Net Ionics Page 4
NET IONIC PREP SESSION KEY
2008B Net Ionic Q4 KEY
Monday, October 27, 2008
2:43 PM
Net Ionics Page 5
NET IONIC PREP SESSION KEY
Net Ionics Page 6
NET IONIC PREP SESSION KEY
2009 Net Ionic Q4 KEY
Thursday, June 25, 2009
10:11 AM
Mean = 8.43 out of 15 points
Net Ionics Page 7
NET IONIC PREP SESSION KEY
Net Ionics Page 8
NET IONIC PREP SESSION KEY
2009B Net Ionic Q4 KEY
Thursday, June 25, 2009
11:01 AM
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NET IONIC PREP SESSION KEY
Net Ionics Page 10
2008B LAB Q5 KEY
Monday, October 27, 2008
2:56 PM
Net Ionics Page 1
Net Ionics Page 2
ID: A
AP* Chemistry: Net Ionic Reactions Prep Session Multiple Choice
Answer Section
OTHER
1. ANS:
D
Most sulfate salts are soluble. Important exceptions to this rule include BaSO 4, PbSO4, Ag2SO4 and
SrSO4.
DIF: Easy
TOP: Chemical Reactions
NOT: 82% answered correctly
2. ANS:
E
MSC: 2002 #11
A coordination complex contains a metal ion with a ligand. It is not unusual for there to be twice the number of
ligands present as the metal’s oxidation number. The combination can be charged or neutral and can be an ion or
a compound.
DIF: Hard
TOP: Chemical Reactions
NOT: 30% answered correctly
3. ANS:
C
MSC: 2002 #12
This is called a disproportionation reaction. Halogens do this well since they can have both positive and negative
oxidation states. Reduction is well...a reduction in oxidation number (gain of electrons) and oxidation is an
increase in oxidation number (loss of electrons).
Br’s Ox #
0
–1
+5
–
–
3 Br 2(aq) + 6 OH (aq) → 5 Br (aq) + BrO3– (aq) 3 H2O(l)
DIF: Easy
TOP: Chemical Reactions
NOT: 67% answered correctly
4. ANS:
B
MSC: 2002 #13
I bet you were looking for a carbon compound being burned. Remember, any nonmetal or nonmetal-nonmetal
covalent compound undergoing combustion will make the oxides of the nonmetals involved.
DIF: Easy
TOP: Chemical Reactions
NOT: 74% answered correctly
MSC: 2002 #14
1
ID: A
MULTIPLE CHOICE
5. ANS: A
Carbonates are generally insoluble, silver carbonate is really insoluble, so it is written “together” or undissociated
in an aqueous solution. Hydrochloric acid is a strong acid, so it completely dissociates in aqueous solution.
Adding acid to a carbonate makes bubbles [classic “volcano reaction”] so CO2 is formed, silver chloride is the
precipitate and water is the final product of the neutralization.
DIF: Hard
TOP: Chemical Reactions
MSC: 1984 #32
NOT: 25% answered correctly
6. ANS: D
It is easier to take the OH– and water out of the equation. Next balance the half-reaction in acid media, then add
hydroxide to each side to neutralize any excess H + ions. Finally cancel waters from one side to “clean up” the
final balanced half-reaction.
The balanced half-reaction is:
CrO2–
→ CrO42– (skeleton without water or OH–)
CrO2– + 2 H2O → CrO42– + 4 H+ + 3 e–
+ 4 OH–
+ 4 OH – (makes 4 waters on the right, cancels 2 waters on the left)
SUM: CrO2– + 4 OH– → CrO42– + 2 H2O + 3 e–
DIF: Easy
TOP: Chemical Reactions
MSC: 1984 #34
NOT: 65% answered correctly
7. ANS: E
Nitrous acid is weak, so it does not dissociate and is written molecularly. Sodium hydroxide is a strong base and
completely dissociates, and sodium is a spectator...so you have HNO 2 + OH–, so far which leads you to answer (E).
To finish it off, you know acid + base yields salt and water, so the salt is sodium nitrite, but again...sodium ion is a
spectator and does not appear in a net ionic reaction.
DIF: Hard
TOP: Chemical Reactions
MSC: 1984 #64
NOT: 27% answered correctly
8. ANS: D
“Excess” stated in a net ionic equation is code for complexation! Copper sulfate is soluble, so the sulfate ion is a
spectator [since none of its “excepts” are present in this reaction]. The complex formed will have the ammonium
ion as a ligand, the oxidation number of copper is doubled to determine how many ligands [note: this doesn’t
always form the most common complex, but it does form a valid complex], so we need 4 ammonia ligands which
are neutral and the complex is [Cu(NH3)4]2+.
DIF: Hard
TOP: Chemical Reactions
NOT: 29% answered correctly
MSC: 1984 #81
2
ID: A
9. ANS: E
Iodide is the ion and is oxidized by whatever is reduced, the permanganate ion in this case.
Permanganate ion is reduced, period.
The oxidation number of manganese changes from +7 to +4, not +2.
Indeed, the oxidation number of the iodide ion is –1 and it changes to zero in iodine.
DIF: Easy
TOP: Chemical Reactions
NOT: 82% answered correctly
10. ANS: D
Red: Cr2O72– + 6 e– + 14 H+ → 2 Cr3+ + 7 H2O
MSC: 1989 #20
DIF: Easy
TOP: Chemical Reactions
MSC: 1989 #22
NOT: 82% answered correctly
11. ANS: E
The reaction: Ca + H2 → CaH2
Calcium hydride is an ionic solid that produces hydrogen gas and calcium hydroxide (hence it’s family name of
alkaline earth metals) when added to water.
DIF: Medium
TOP: Chemical Reactions
MSC: 1989 #44
NOT: 40% answered correctly
12. ANS: E
An oxidizing agent is itself reduced and it must be a reactant. Therefore, the permanganate ion is the oxidizing
agent. The chlorite ion is the reducing agent since it is oxidized.
DIF: Easy
TOP: Chemical Reactions
MSC: 1994 Q#18
NOT: 62% answered correctly
13. ANS: A
There just a series of “stuff” to memorize to get redox reactions correct. These are summarized in your net ionic
equation notes. In basic media, dichromate ion is oxidized to chromate ion while in acid media, dichromate is
oxidized to Cr3+ ion.
DIF: Hard
TOP: Chemical Reactions
MSC: 1994 Q#29
NOT: 36% answered correctly
14. ANS: B
Metal oxides are ionic solids at room temperature and are also basic anhydrides (react with water to form
bases--dependent upon solubility). Nonmetal oxides are more likely to be gases at room temperature and are acidic
anhydrides, especially SOx and NOx (pronounced “socks and knocks) which are responsible for acid rain.
DIF: Easy
TOP: Chemical Reactions
MSC: 2002 #32
NOT: 69% answered correctly
15. ANS: B
“Oxidizing agent” is code for “is itself reduced”. Copper’s oxidation number increases, so it is definitely not
reduced. Statement II is true. Hydrogen ions and the hydrogen atoms of water both have oxidation states of +1.
DIF: Medium
TOP: Chemical Reactions
NOT: 49% answered correctly
MSC: 2002 #51
3
ID: A
16. ANS: B
The balanced equation is : C3H8 + 5 O2 → 3 CO2 + 4 H2O
DIF: Easy
TOP: Chemical Reactions
NOT: 71% answered correctly
17. ANS: C
MSC: 2002 #52
Carbonates are frequently insoluble. Group II carbonates (Ca, Sr, and Ba) are insoluble. Some other
insoluble carbonates include FeCO3 and PbCO3.
DIF: Medium
TOP: Chemical Reactions
NOT: 45% answered correctly
MSC: 2002 #65
4